In general, inkjet printing machines or printers include at least one printhead that ejects drops or jets of liquid ink onto a recording or image forming surface. An aqueous inkjet printer employs water-based or solvent-based inks in which pigments or other colorants are suspended or in solution. Once the aqueous ink is ejected onto an image receiving surface by a printhead, the water or solvent is evaporated to stabilize the ink image on the image receiving surface. When aqueous ink is ejected directly onto media, the aqueous ink tends to soak into the media when it is porous, such as paper, and change the physical properties of the media. To address this issue, indirect printers have been developed that eject ink onto a blanket mounted to a drum or endless belt. The ink is dried on the blanket and then transferred to media. Such a printer avoids the changes in media properties that occur in response to media contact with the water or solvents in aqueous ink. Indirect printers also reduce the effect of variations in other media properties that arise from the use of widely disparate types of paper and films used to hold the final ink images.
In these indirect printers, the blanket surface must wet well enough to prevent significant coalescence of the ink on the surface and also facilitate the release of the ink from the blanket to the media after the ink has dried on the blanket. Applying a coating material to the blanket can facilitate the wetting of the blanket surface and the release of the ink image from the blanket surface. Coating materials have a variety of purposes such as wetting the blanket surface, inducing solids to precipitate out of the liquid ink, providing a solid matrix for the colorant in the ink, aiding in the release of the printed image from the blanket surface, or the like. In certain systems both the coating material and the layers of ink on the blanket surface can adhere to the media on which the printed image has been transferred from the blanket surface. Because the coating material and the layers of ink can be prone to high adhesion, image defects can arise from unreliably stripping of the media from the blanket surface. Image defects can degrade the final image quality. Reliable methods of stripping the media from the blanket surface would be beneficial.
In previously known indirect printers, air knives have been used to enable stripping of the media from the blanket surface. However, in printers with an insufficient lead edge separation of the media from the blanket surface, air knives may not reliably strip the media from the blanket surface because adhesion of the media to the blanket surface can be high. Certain previously known printers use stripper fingers to enable stripping of the media from the blanket surface. However, stripper fingers may prove unreliable because the lead edge of the media may have little or no separation from the blanket surface. Consequently, pressure may be needed to press the stripper fingers onto the blanket surface to urge the fingers between the blanket and media; however, these pressures may cause the fingers to affect the blanket surface adversely and shorten the life to the blanket. Certain previously known printers use small bend radii to enhance separation of the media from transfer surfaces or fusing surfaces. However, some printers have too large of a radius to encourage self-stripping. In other printers, such as printers with a belt architecture, the bending of the blanket belt around a small radius can lead to issues such as belt cracking and fatigue failure. Improvements in aqueous indirect inkjet printers that enable more reliable stripping of the media from the blanket surface are desirable.